Works quietly with line worker (5)
I believe the answer is:
plant
'works' is the definition.
(synonyms)
'quietly with line worker' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'with' is a charade indicator (letters next to each other).
'line' becomes 'l' (used when specifying particular lines from a poem).
'worker' becomes 'ant' (worker is a type of ant).
'p'+'l'+'ant'='PLANT'
(Other definitions for plant that I've seen before include "Hide in order to be found" , "Factory - bit of vegetation" , "Set; factory" , "Put in the ground to grow" , "Factory; informer" .)